JP7567447B2 - Meltblown nonwoven fabrics and air filters - Google Patents

Description

The present invention relates to a melt-blown nonwoven fabric that has excellent dimensional stability during processing.

Conventionally, air filters have been used to remove pollen, dust, and the like from the air, and nonwoven fabrics are often used as the filter material for these air filters. In particular, the melt-blowing method, which is one of the methods for manufacturing nonwoven fabrics, is widely used in the manufacture of filter materials for air filter products, battery separators, and the like. In the melt-blowing method, a thermoplastic polymer extruded from a spinneret is generally thinned into fibers by spraying hot air, and the self-fusion properties of the resulting fibers are utilized to form a fiber web.

Compared to other nonwoven fabric manufacturing methods such as the spunbond method, the meltblowing method does not require complicated steps and has the advantage of easily producing fine fibers with single fiber diameters of tens of microns to a few microns or less.

The performance required of an air filter here is a high collection efficiency that can capture a large amount of microscopic dust particles, and low pressure loss that provides little resistance when gas passes through the inside of the air filter. In order to obtain a filter medium with high collection efficiency, it is suitable for the single fibers that make up the nonwoven fabric to be fine. However, when the single fibers are made finer, the nonwoven fabric becomes more easily crushed, and there is an issue that the pressure loss increases due to the increased fiber density of the nonwoven fabric.

In addition, to obtain a filter medium with low pressure loss, it is suitable for the single fibers that make up the nonwoven fabric to be thick, but on the other hand, there is a problem in that if the single fibers are made thicker, the fiber surface area in the nonwoven fabric decreases, resulting in a decrease in collection efficiency. Thus, in the performance required of air filters in conventional technology, high collection efficiency and low pressure loss are in a contradictory relationship.

As a method for solving the above problems, attempts have been made to simultaneously achieve high collection efficiency and low pressure loss by making nonwoven fabric into an electret and utilizing electrostatic effects in addition to physical effects (see Patent Documents 1, 2, and 3). Furthermore, a heat-resistant electret material has been proposed by adding a hindered amine additive to the fibers that make up the nonwoven fabric (see Patent Document 4).

Japanese Unexamined Patent Publication No. 61-289177 U.S. Patent No. 6,119,691 JP 2003-3367 A Japanese Unexamined Patent Publication No. 63-280408

As described above, the collection performance is improved by making the nonwoven fabric into an electret, and the thermal stability is further improved by adding a hindered amine-based additive, but the nonwoven fabric's elongation increases, and it has been found that the following problems arise. When manufacturing nonwoven fabric as a filter medium, tension is applied to the nonwoven fabric in various processes such as molding or functionality-imparting processing, and the nonwoven fabric is wound up into a roll or laminated with a reinforcing material. If the elongation of the nonwoven fabric increases, problems arise in that when force is applied to the nonwoven fabric as described above, it becomes wider and its processability becomes very poor.

In view of the above problems, the present invention aims to provide a melt-blown nonwoven fabric that has excellent dimensional stability and good processability, and an air filter using the same.

As a result of intensive research conducted by the present inventors in order to solve the above problems, they have completed the present invention having the following configuration.
1. A melt-blown nonwoven fabric, containing 0.01 to 3 parts by weight of a hindered amine additive and 0.025 to 0.25 parts by weight of a fatty acid metal salt, based on 100 parts by weight of the resin forming the nonwoven fabric, and having a breaking elongation [%] divided by the basis weight [g/ ^m2 ] in a tensile test of 0.5 to 4.0.
2. The melt-blown nonwoven fabric according to 1, characterized in that the value obtained by dividing the breaking strength [N/50 mm] in a tensile test by the basis weight [g/m ² ] is 0.2 to 1.0. 3. The melt-blown nonwoven fabric according to 1 or 2, characterized in that it has been made into an electret.
4. An air filter comprising the melt-blown nonwoven fabric according to any one of 1 to 3.

According to the above configuration of the present invention, the value of the breaking elongation in a tensile test divided by the basis weight is 0.5 to 4.0, so it is possible to provide a nonwoven fabric for filters that has excellent dimensional stability during processing.

The melt-blown nonwoven fabric of the present invention contains 0.01 to 3 parts by weight of a hindered amine additive and 0.025 to 0.25 parts by weight of a fatty acid metal salt, assuming that the resin forming the nonwoven fabric is 100 parts by weight. It has been found that by containing 0.01 to 3 parts by weight of a hindered amine additive and 0.025 to 0.25 parts by weight of a fatty acid metal salt, excellent dimensional stability and high processability are achieved, as shown in the examples described below.

The content of the hindered amine additive is 0.01 to 3 parts by weight per 100 parts by weight of the resin constituting the nonwoven fabric, and from the standpoint of processability, charge retention effect, and uniformity as a material, it is preferable that the content be 0.7 to 1.5 parts by weight. Specific examples of hindered amine stabilizers include poly[{(6-(1,1,3,3-tetramethylbutyl)imino-1,3,5-triazine-2,4-diyl}{(2,2,6,6-tetramethyl-4-piperidyl)imino}hexamethylene{(2,2,6,6-tetramethyl-4-piperidyl)imino}], dimethyl succinate-1-(2-hydroxyethyl)-4-hydroxy-2,2,6,6-tetramethylpiperidine polycondensate, and bis(1,2,2,6,6-pentamethyl-4-piperidyl)-2-n-butylmalonate.

The content of the fatty acid metal salt is 0.025 to 0.25 parts by weight, and preferably 0.03 to 0.1 parts by weight, per 100 parts by weight of the resin constituting the nonwoven fabric. Specific examples of the fatty acid in the fatty acid metal salt include stearic acid, lauric acid, myristic acid, palmitic acid, etc., and examples of the metal element include magnesium, sodium, potassium, aluminum, zinc, etc.

The melt-blown nonwoven fabric of the present invention has a value of breaking elongation [%] divided by basis weight [g/m ² ] of 0.5 to 4.0, preferably 1.0 to 3.5. If the value of breaking elongation divided by basis weight exceeds 4.0, the nonwoven fabric will be wound up or laminated with a reinforcing material in the manufacturing process of a filter using the nonwoven fabric as a filter medium, resulting in poor handling. If the value is below 0.5, the nonwoven fabric will not be flexible and will break during pleating, which will be a problem. If the value is in the range of 0.5 to 4.0, the nonwoven fabric will be less prone to breaking during processing, and improved processability and workability can be expected.

Here, the breaking elongation is measured by pulling a nonwoven fabric sample using a tensile tester and measuring the elongation at the time the sample breaks (breaks). The breaking elongation (tensile elongation) is calculated by the following formula.
Breaking elongation [%] = 100 × (L - L0) / L0
L0: length of sample before test, L: length of sample just before break

Furthermore, the melt-blown nonwoven fabric of the present invention has a breaking strength [N/50 mm] divided by the basis weight [g/m ² ] of 0.2 to 1.0, preferably 0.3 to 0.7. When the breaking strength divided by the basis weight is in the range of 0.2 to 1.0, improved processability and workability can be expected.

Here, breaking strength refers to the maximum strength when a nonwoven fabric sample is pulled to break using a tensile tester.

The raw material of the melt-blown nonwoven fabric of the present invention can be a thermoplastic resin that can be melt-spun. For example, polyolefin resins such as polyvinyl chloride, polyvinylidene chloride, acrylic, polypropylene, low-density polyethylene, high-density polyethylene, linear low-density polyethylene, copolymerized polypropylene (for example, a binary or multi-component copolymer of propylene with ethylene, butene, 1,4-methylpentene-1, etc.), polyethylene terephthalate, polybutylene terephthalate, polyester resins such as these low-melting polyesters copolymerized with isophthalic acid in addition to terephthalic acid as an acid component, polyamide resins such as nylon 6 and nylon 66, polystyrene (atactic polystyrene, syndiotactic polystyrene), polyurethane elastomers, polyester elastomers, polytetrafluoroethylene, and other thermoplastic resins. In addition, functional resins can be used, such as those that are biodegradable using biodegradable resins such as lactic acid-based polyesters. In addition, copolymers containing these as the main components and blends of multiple of these polymers can be used.

In addition to the hindered amine additive, the melt-blown nonwoven fabric of the present invention may contain additives such as nitrogen-containing hindered phenols, metal salt hindered phenols, phenols, sulfur, and phosphorus. Furthermore, the melt-blown nonwoven fabric of the present invention may contain various additives such as matting agents, lubricants, pigments, heat stabilizers, light resistance agents, UV absorbers, electrostatic agents, conductive agents, and heat storage materials within an appropriate range, as necessary. In addition, additives having various functions such as dust removal, deodorization, antibacterial, antifungal, antiviral, insect repellent, insecticide, pest repellent, harmful substance removal, fragrance, dehumidification, humidity control, moisture absorption (drying), moisture (humidity) permeation, adsorption of oils, etc., ion balance adjustment such as cation adsorption, and evaporation or sustained release of water and volatile drugs, etc. may be added.

The fiber form of the meltblown nonwoven fabric may be a single-phase form consisting of a single polymer, or a composite form consisting of multiple types of the polymer (core-sheath composite form, parallel composite form, split fiber composite form).

The cross-sectional shape of the fiber is not limited to a circular cross-section, but may be an ellipse, a diamond, a triangle, a T-shape, etc., or may have a hollow portion, and any shape may be selected as appropriate.

The meltblown nonwoven fabric of the present invention is preferably electretized by known techniques such as corona discharge and water flow charging, since this allows for the production of filter media and air filters with even higher performance. When an electret nonwoven fabric that does not contain a hindered amine additive comes into contact with water, it usually loses its charge. It has been found that an electret nonwoven fabric that contains a hindered amine additive does not easily lose its charge even when it comes into contact with water.

The basis weight of the meltblown nonwoven fabric of the present invention is preferably 5 to 100 g/m ² , more preferably 10 to 60 g/m ^2. The fiber diameter is 0.001 to 100 μm, preferably 0.005 to 20 μm, more preferably 0.01 to 10 μm, even more preferably 0.02 to 5 μm, and particularly preferably 0.03 to 3 μm. If the fiber diameter exceeds 100 μm, it is difficult to obtain a practical collection efficiency as an air filter, and the efficiency is greatly reduced during charge decay. If the fiber diameter is smaller than 0.001 μm, it is difficult to impart an electrostatic charge as an electret material.

The fibers of the meltblown nonwoven fabric of the present invention may be homogeneous and made from a single manufacturing method and material, or may be a mixture of two or more fibers with different manufacturing methods, materials, and fiber diameters.

The air filter of the present invention uses the melt-blown nonwoven fabric of the present invention, and may be subjected to, for example, shaping or attachment to a frame. The air filter of the present invention may also be formed by combining the melt-blown nonwoven fabric of the present invention with other materials.

When an air filter is manufactured using the melt-blown nonwoven fabric of the present invention as a filter material, it may be processed into a wavy shape. Methods for processing into a wavy shape include repeated folding into peaks and valleys, generally known as pleating, and wavy processing of the core in cardboard processing. By processing into a wavy shape in this way, the filtration area can be increased for a given ventilation area, and the pressure loss is reduced as the speed of air passing through the air filter for a specific air volume decreases, improving breathability. Furthermore, improved collection efficiency and longer life are achieved, and the strength of the air filter itself is increased compared to when it is used as a single plate, which has the advantage of making it easier to handle when installing it in an air conditioner or when replacing it.

As described above, the present invention provides a melt-blown nonwoven fabric and air filter that exhibits little loss of charge when heated, i.e., excellent thermal stability, and excellent dimensional stability during processing.

The present invention will be specifically explained below with reference to examples. However, the present invention is not limited to the following examples, and can be modified as appropriate within the scope of the above and below-mentioned aims. Such modifications are also included within the technical scope of the present invention.

First, the characteristic values measured in the examples and comparative examples and the methods for measuring them are shown below.

(Melt flow index [g/10 min])
Measured according to JIS K6921-2:2018, Table 3, 1.1 Melt mass flow rate (MFR).

(Average fiber diameter (μm))
Ten small pieces of sample were randomly taken from the melt-blown nonwoven fabric, and photographs were taken at 500 to 3000 times magnification using a scanning electron microscope. The fiber diameters of 10 fibers from each sample, for a total of 100 fibers, were measured, and the average value was calculated. Calculations were rounded off to the first decimal place.

(Weight (g/ ^m2 ))
In accordance with JIS L1906 (2000 edition) 5.2, three samples of melt-blown nonwoven fabric measuring 50 cm in the longitudinal direction and 50 cm in the transverse direction were taken, and the weight of each sample was measured. The average value obtained was converted to a value per unit area, and the value was rounded off to the first decimal place.

(Processability)
Activated carbon particles (particle size 200 to 400 μm) were scattered on a general reinforcing material, and melt-blown nonwoven fabric was layered and bonded to produce an activated carbon sheet. This sheet was pleated using a reciprocating pleating machine to a pleat height of 3.0 cm, and was evaluated according to the following criteria.
◯: The pleats are uniform and there are no problems with processing.
△: The pleats are slightly uneven.
x: There is a problem in processing, either the pleats are uneven or the nonwoven fabric is torn.

(Breaking strength, breaking elongation)
According to 5.3.1 of JIS L1906 (2000 edition), tensile tests were performed on three samples in both the longitudinal and transverse directions under the conditions of a sample size of 5 cm × 20 cm, grip interval of 15 cm, and tensile speed of 20 cm/min. The maximum strength when the sample was pulled until it broke was defined as the breaking strength [N/50 mm], and the elongation at break was defined as the breaking elongation [%], and the values were calculated by dividing each by the basis weight of the sheet [g/ ^m2 ].

[Example 1]
A meltblown nonwoven fabric (basis weight 20 g/m ² , average fiber diameter 2.0 μm, thickness 0.23 mm) was produced containing 1.0 part by weight of hindered amine additive Chimassorb 944 (manufactured by BASF) and 0.05 part by weight of magnesium stearate per 100 parts by weight of polypropylene resin with a melt flow index of 1300. The obtained nonwoven fabric had a breaking strength per basis weight of 0.7 and a breaking elongation per basis weight of 2.0. The processability was rated as ◯.
[Example 2]
A meltblown nonwoven fabric (basis weight 45 g/m ² , average fiber diameter 3.5 μm, thickness 0.35 mm) was produced containing 1.0 part by weight of hindered amine additive Chimassorb 944 (manufactured by BASF) and 0.05 part by weight of magnesium stearate per 100 parts by weight of polypropylene resin with a melt flow index of 1300. The obtained nonwoven fabric had a breaking strength per basis weight of 0.3 and a breaking elongation per basis weight of 3.5. The processability was rated as good.
[Comparative Example 1]
A melt-blown nonwoven fabric (basis weight 20 g/m ² , average fiber diameter 2.0 μm, thickness 0.23 mm) was produced containing 1.0 part by weight of a hindered amine additive, Chimassorb 944 (manufactured by BASF Corporation), per 100 parts by weight of polypropylene resin with a melt flow index of 1300. The resulting nonwoven fabric had a breaking strength per basis weight of 0.3 and a breaking elongation per basis weight of 0.3. The processability was rated as x.
[Comparative Example 2]
A meltblown nonwoven fabric (basis weight 20 g/m ² , average fiber diameter 2.0 μm, thickness 0.23 mm) was produced containing 1.0 part by weight of a hindered amine additive, Chimassorb 944 (manufactured by BASF), and 0.01 part by weight of magnesium stearate, per 100 parts by weight of polypropylene resin with a melt flow index of 1300. The resulting nonwoven fabric had a breaking strength per basis weight of 0.5 and a breaking elongation per basis weight of 0.2. The processability was poor.

The meltblown nonwoven fabrics of Examples 1 and 2 are found to have superior processability compared to Comparative Examples 1 and 2.

The meltblown nonwoven fabric of the present invention has excellent heat resistance and dimensional stability during processing, making it suitable for use as a filter material for air filters.

Claims (4)

A melt-blown nonwoven fabric, characterized in that it contains 0.01 to 3 parts by weight of a hindered amine additive and 0.025 to 0.25 parts by weight of a fatty acid metal salt, relative to 100 parts by weight of the resin that forms the nonwoven fabric, and has a breaking elongation [%] divided by the basis weight [g/ ^m2 ] in a tensile test of 0.5 to 4.0. The melt-blown nonwoven fabric according to claim 1, characterized in that the value obtained by dividing the breaking strength [N/50 mm] in a tensile test by the basis weight [g/m ² ] is 0.2 to 1.0. The meltblown nonwoven fabric according to claim 1 or 2, characterized in that it is electret. An air filter comprising the melt-blown nonwoven fabric according to any one of claims 1 to 3.